A friend at a party asked him what the name of the next Tesla would be after the S and X. Musk joked, "the Model E." And the name kinda stuck.

They applied for a trademark on "E", and as another joke, applied for a Model Y (rimshot) trademark.

Ford was apparently not pleased about the "E" filing, and according to Musk, threatened to sue Tesla. It's not entirely clear why, aside from the fact that Ford's seminal models – the Model A and Model T – had a similar naming scheme.

Since then, Tesla has pulled its trademark for the E, with Musk saying today that, "Ford tried to kill sex."